This invention relates to processes for foaming polymeric compositions and to foamed polymeric compositions.
Foamed polymeric compositions are cellular structures which are typically comprised of a gaseous compound dispersed throughout a solid. Such foamed compositions can exhibit a lower density and weight, but a substantially equivalent strength to non-foamed compositions. An example of a commercial foamed thermoplastic polymeric composition is a polycarbonate polymer foamed with 5-phenyl tetrazole compound.
Polycarbonate polymers are derived from reactions of dihydroxyorganic compounds. Commonly used polycarbonates are derived from dihydric phenols and carbonic acids such as phosgene. Such thermoplastic polymers are suitable for the manufacture of molded parts wherein impact strength, rigidity, toughness, heat resistance and excellent electrical properties are desired.
Thermoplastic polymeric compositions are foamed by incorporating a blowing or foaming agent into the polymeric composition at a temperature below the decomposition temperature of the blowing agent. The polymeric composition and blowing agent are then subjected to sufficient conditions to decompose the agent into gaseous products, for example by raising temperature, which can cause the volume of the polymeric composition to increase. Unfortunately, many blowing agents, including 5-phenyl tetrazole, decompose into products which adversely affect the polymeric composition. For example, the decomposition products of 5-phenyl tetrazole undesirably react with polycarbonate polymers, lowering the molecular weight, and causing brittleness in the final polycarbonate foam.
In view of the disadvantages of known methods, it would be desirable to have blowing agents, and/or a method of foaming polymeric compositions wherein the agents would be versatile for a variety of polymeric compositions, and would have degraded products which would not react with polymeric compositions.